Process for retrofitting an industrial gas turbine engine for increased power and efficiency

ABSTRACT

A process for retrofitting an industrial gas turbine engine of a power plant where an old industrial engine with a high spool has a new low spool with a low pressure turbine that drives a low pressure compressor using exhaust gas from the high pressure turbine, and where the new low pressure compressor delivers compressed air through a new compressed air line to the high pressure compressor through a new inlet added to the high pressure compressor. The old electric generator is replaced with a new generator having around twice the electrical power production. One or more stages of vanes and blades are removed from the high pressure compressor to optimally match a pressure ratio split. Closed loop cooling of one or more new stages of vanes and blades in the high pressure turbine is added and the spent cooling air is discharged into the combustor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit to U.S. Provisional Application62/299,248 filed on Feb. 24, 2016 and entitled PROCESS FOR RETROFITTINGAN INDUSTRIAL GAS TURBINE ENGINE FOR INCREASED POWER AND EFFICIENCY.

GOVERNMENT LICENSE RIGHTS

This invention was made with Government support under contract numberDE-FE0023975 awarded by Department of Energy. The Government has certainrights in the invention.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to a power plant with anindustrial gas turbine engine, and more specifically to a process forretrofitting an industrial gas turbine engine for increased power andefficiency.

Description of the Related Art including information disclosed under 37CFR 1.97 and 1.98

Single shaft gas turbine engines are limited in power and efficiencywhen pressure ratios and firing temperatures are raised to the pointwhere the last turbine stage is loaded to where Mach numbers reach themaximum aerodynamic capability. In these cases, the engine has limitedcapability to be upgraded for either power or efficiency. In some cases,the two shaft engine configuration is coupled to a larger free spinningturbine with the generator on the low speed shaft to create an upgradein power. This also has limitations in total flow and is limited in themaximum pressure ratio that the unit could sustain.

BRIEF SUMMARY OF THE INVENTION

In the present invention, existing single shaft turbine engines areretrofitted with a low speed turbine coupled to a low speed compressorthat is aerodynamically coupled in front of the existing compressor, nowdeemed the high compressor, where the existing turbine (now deemed thehigh pressure turbine) is coupled to the low speed turbine. Furtherenhancements to the cooling systems enhance the ability to increase thefiring temperature of the existing section of the gas turbine andelevate the overall power rating and efficiency.

A process for retrofitting an industrial gas turbine engine in which anew independently operated low spool shaft with a power turbine and alow pressure compressor is installed with the low pressure compressedair being directed into an inlet of the high pressure compressor. Avariable area turbine vane assembly is added to the power turbine and avariable inlet guide vane to the low pressure compressor. In anotherembodiment, a power turbine that drives an electric generator isretrofitted by using the power turbine to drive a low pressurecompressor that feeds low pressure air to an inlet of the high pressurecompressor, and relocates the electric generator to the high speed shafton a cold end of the compressor. Regenerative or closed loop cooling canalso be used to increase efficiency by bleeding off air from thecompressor, cooling the air and then pressurizing the air further inorder to pass through stator vanes for cooling, where the spent coolingair is then discharged into the combustor upstream of the flame. Air forcooling can be bled off from a middle stage of the compressor or fromthe exit end of the compressor. Or, ambient air from atmosphere can beused with an external compressor to further compress the air to P3 levelfollowed by intercooling prior to cooling of the stator vanes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a single shaft industrial gas turbine engine that drives anelectric generator of the prior art.

FIG. 2 shows a retrofitted industrial gas turbine engine with a lowspeed low pressure turbine and low pressure compressor of the presentinvention.

FIG. 3 shows a turbine exhaust system for a retrofitted engine of thepresent invention.

FIG. 4 shows a single shaft retrofitted industrial gas turbine enginewith at least one of the high pressure compressor stage removed.

FIG. 5 shows a prior art two shaft industrial gas turbine engine with alow speed power turbine driving an electric generator.

FIG. 6 shows a retrofitted two shaft industrial gas turbine engine withan electric generator and an optional gearbox on the high speed shaft ofthe present invention.

FIG. 7 shows a low spool retrofitted with a high pressure turbine havingregenerative cooling of the present invention.

FIG. 8 shows a single shaft industrial gas turbine engine comprising aturbine vane cooling system retrofit with bleed air from the compressorintercooled and then further compressed with regenerative cooling beforedischarge into the combustor of the present invention.

FIG. 9 shows an industrial gas turbine engine comprising a turbine vanecooling system retrofit with ambient air compressed and then cooled toprovide cooling for a row of stator vanes in the turbine beforedischarge into the combustor of the present invention.

FIG. 10 shows an industrial gas turbine engine comprising a turbine vanecooling system retrofit with bleed air intercooled and then furthercompressed for use in turbine vane cooling and then discharged into thecombustor of the present invention.

FIG. 11 shows an industrial gas turbine engine comprising a turbine vanecooling system retrofit with bleed air compressed and then intercooledfor use in turbine vane cooling and then discharged into the combustorof the present invention.

FIG. 12 shows an industrial gas turbine engine comprising a turbine vanecooling system retrofit with compressed air further compressed and thenintercooled for use in turbine vane cooling and then discharged into thecombustor of the present invention.

FIG. 13 shows an industrial gas turbine engine comprising a turbine vanecooling system retrofit with bleed air compressed and then intercooledfor use in turbine vane cooling and then discharged into the combustorof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a process for retrofitting an industrial gasturbine engine of a power plant for increased power and efficiency.

In the present invention, existing single shaft turbine engines 10 likethat shown in FIG. 1 are retrofitted with a low speed turbine (LST)coupled to a low speed compressor (LSC) that is aerodynamically coupledin front of the existing compressor, now deemed the high pressurecompressor (HPC), where the existing turbine (now deemed the highpressure turbine or HPT), is coupled aerodynamically to the low speedturbine (LST). The existing single shaft industrial gas turbine engineincludes a compressor 11 driven by a turbine 13 with a combustor 12, andan electric generator 14 driven by the rotor on the cold side which isin front of the compressor 11. Bearings 15 support the rotor of theengine.

Further enhancements to the cooling systems enhance the ability toincrease the firing temperature of the existing section of the gasturbine and elevate the overall power rating and efficiency. Theretrofit-able upgrade consists of several optional elements. Most or allof the cooling air used to cool turbine airfoils is discharged into thecombustor upstream of the flame instead of into the hot gas path of theturbine in order to improve the efficiency of the engine. In oneembodiment, some of the turbine airfoil cooling air can be dischargedthrough trailing edge exit holes and into the hot gas stream with mostof the spent cooling air being discharged into the combustor. Passingcooling air through the turbine airfoil for cooling and then dischargingmost or all of the spent cooling air is referred to as a closed loopcooling where the cooling circuit in the turbine airfoil is a closedloop instead of an open loop in which all of the cooling air isdischarged out from the airfoil and into the hot gas stream through filmholes or exit holes in the airfoil.

The first upgrade element is to introduce a low speed turbine (LST) 21directly driving a low speed compressor (LSC) 22 is coupledaerodynamically to the existing single shaft industrial gas turbineengine (IGTE) 10. The existing industrial gas turbine exhaust system isremoved and replaced with a close coupled turbine section featuring avariable area low pressure turbine stator vane (turbine 21 with variableturbine inlet guide vanes 25). This variable turbine stator vane 25 isused in conjunction with the low compressor variable geometry, Inletguide vane and variable geometry Stator guide vanes part of compressor22, to control the low shaft speed and to simultaneously match the lowspeed and the high speed compressor for aerodynamic performance (FIG.2).

The discharge of the low pressure compressor 22 is connectedaerodynamically to the inlet of the existing compressor 11 through acompressed air line 23, now the high pressure compressor 11, boostingthe overall pressure ratio of the engine. The generator connected to theoriginal gas turbine is now defined as being on the high speed shaft, asthe new turbine 21 and compressor 22 make the low speed shaft.

The existing gas turbine has the exhaust diffuser removed and is closecoupled to the new low pressure gas turbine 21 with the variable areaturbine stator vane 25. The flow discharging the existing gas turbine 13now enters the low pressure gas turbine 21 which passes through thevariable area turbine stator vane 25 and passes across the low speedturbine and out the new exhaust system (FIG. 3). A turbine exhaust duct26 is installed to pass the high pressure turbine exhaust into the lowpressure turbine and variable inlet guide vanes 25.

The retrofit in this configuration can increase the existing industrialengines overall pressure ratio significantly, a range from 1.1 to evenover 7×, thus greatly enhancing the engines mass flow and power output.The upgrade including the new low pressure gas turbine 21 may entailremoving one or more of the front high pressure compressor bladingstages 11A to optimally match the pressure ratio split between the lowpressure and high pressure compressors 11A and 22 (FIG. 4). A new inlet24 to the high pressure compressor 11A is also added to receive thecompressed air from the low pressure compressor 22. To get the maximumpower out of the upgraded engine and higher efficiency at low powermodes, variable inlet guide vane assemblies are used in the highpressure compressor and the low pressure compressor and the low pressureturbine in order to control flows.

An alternate embodiment of this invention is to retrofit a two shaft gasturbine, where the high speed shaft has a compressor 11 and turbine 13on one shaft, and a low speed turbine (Power turbine) 15 driving agenerator 14 or mechanically driven equipment (Pump, process compressoretc.) as shown in the FIG. 5 embodiment. In the FIG. 6 embodiment, thepower turbine 21 is used to drive a low speed compressor 22 that isconnected aerodynamically to the existing compressor 11 (Now deemed thehigh pressure compressor) through compressed air line 23. The generator14 is moved to the high speed shaft connected on the cold end of thehigh pressure compressor 11. In the FIG. 6 embodiment, one or morestages of the front of the high pressure compressor 11A would be removedin order to match a pressure ratio split between the LP compressor 22and the HP compressor 11A.

In the process for retrofitting the prior art IGT engines in FIGS. 1 and5, the old electric generator would require replacement since theretrofitted IGT engine would then produce around twice the power as theold engine and thus require a new electric generator. For example, if aprior art IGT single spool engine of FIG. 1 which is capable ofproducing 300 MW of power is retrofitted, the new IGT engine would becapable of producing twice that power or 600 MW. Thus, the old 300 MWelectric generator would need to be replaced with a 600 MW electricgenerator. The old 300 MW electric generator could be reused, but asecond 300 MW generator would have to be added in which both generatorswould be driven by the same output shaft. This modification wouldprobably be more costly than replacing the old 300 MW generator with anew modern 600 MW generator. In limited upgrade cases, the old electricgenerator can still be used with a slightly more powerful industrialengine upgrade. The electric generator is chosen that has the capabilityof producing more electrical energy than the IGT engine operating at astandard operating temperature so that when a cold day occurs and theengine can produce more power, the electric generator can produce morepower. Thus, if an IGT engine upgrade does not produce more power thanthe electric generator is capable of producing, then the old electricgenerator can still be used in the upgraded IGT engine.

The second upgrade elements are cooling system retrofits and are alsoavailable to be created alone, or in combination with the low speedspool retrofit. This use of regenerative (closed loop) cooling for thefirst several rows of cooled turbine vanes in the now high speed turbine13 are implemented where the existing turbine stator vanes with coolingflow discharges into the gas path (such as through film cooling holes orexit holes) are replaced by stator vanes that collect the post coolingcoolant and return it into the combustor 12 upstream of the flame. Theuse of the regenerative or closed loop cooling increases the thermalefficiency of the engine, and further enhances the overall power andefficiency coupled with the low speed compressor 22 and turbine shaft(FIG. 7). Cooling air line 27 passes the spent turbine vane cooling airinto the combustor 12.

The cooling system if upgraded alone, would source cooling air from oneof several places. This first option would be from ambient air such asthat in FIG. 9 with the external cooling air compressor 33 driven by amotor 32 would raise the cooling air pressure to the required level.

In the FIG. 8 embodiment, the cooling air compression could be partiallycompressed (bled off from a stage of the HPC 11), intercooled with anintercooler 31, and further compressed for reduced compressor work andincreased compressor efficiency, and then to reduce the cooling aircompressor to the desired coolant temperature. Cooling air is bled offfrom a stage of the compressor 11, passed through an intercooler 31, andthen boosted in pressure by compressor 33 so that enough pressureremains in the cooling air after passing through the stator vanes inorder to discharge the spent cooling air into the combustor 12. Coolingair passage 34 from the compressor 11 can come from the compressor exitor from an earlier stage which is at a lower pressure than the exitdischarge pressure.

A second approach is shown in FIG. 9 where this ambient sourced air iscompressed and then cooled in an intercooler to the desired cooling airtemperature. In this second case the cooling air work of compression ishigher than in the FIG. 8 embodiment, however the configuration could bemade simpler. In the third and fourth case the cooling air is bled fromone of the existing compressor bleed ports where the flow is bothintercooled and recompressed in the third case, or compressed andafter-cooled being the fourth case, FIGS. 10 and 11.

A fifth case the fully compressed air from the main compressor isextracted and cooled and then further compressed, FIG. 12. A sixthoption is extracting the cooling air from the compressor exit andfurther compressing followed by post cooling to the desired cooling airtemperature for vane cooling, FIG. 13.

In each of these cases the externally compressed cooling air is createdat a pressure significantly over the main compressor 11 dischargepressure, commonly designated P3. This intercooled and over pressurizedcoolant provides optimized low temperature high pressure coolant to theturbine stator vanes to provide cooling of the vanes to the desiredlevel while the captured cooling flow exiting the vane exists withpositive pressure margin to pass it into the combustor shell to mix withthe existing compressor discharge air.

This configuration of closed loop air cooing (meaning most or all of theairfoil cooling air is discharged into the combustor instead of the hotgas stream through the turbine) optimized thermal efficiency andaugments power by increasing the overall flow through the combustorwhile preventing coolant form diluting the main hot gas stream. Byclosed loop cooling of the turbine airfoil, the present invention meansthat most or all of the spent cooling air passing through the turbineairfoils is discharged into the combustor instead of being dischargedinto the hot gas stream.

In the cases where the regenerative turbine vane cooling implemented onthe HPT is coupled with the low spool turbine and compressor, thecooling air source could be from the LPC discharge, or from anintermediate LPC bleed, HPC bleed or the HPC compressor discharge.

We claim the following:
 1. A process for retrofitting an industrial gasturbine engine of a power plant, the industrial gas turbine enginehaving a main compressor driven by a main turbine and an electricgenerator either driven by the main compressor or by a power turbinedriven by the main turbine, the process comprising the steps of: addinga new inlet to the main compressor capable of receiving a greater airflow; adding a low spool with a low pressure turbine driving an lowpressure compressor to the main turbine such that the low pressureturbine is driven by exhaust from the main turbine; adding a variableinlet guide vane assembly to an inlet side of the low pressure turbine;adding a compressed air line connecting the low pressure compressor tothe new inlet of the main compressor such that compressed air from thelow pressure compressor flows into the main compressor; and, replacingthe electric generator with a new electric generator that has aroundtwice the electrical power production.
 2. The process for retrofittingan industrial gas turbine engine of a power plant of claim 1, andfurther comprising the steps of: removing at least one stage of rotorblades and stator vanes from the main compressor to optimally match apressure ratio split between the low pressure compressor and the maincompressor.
 3. The process for retrofitting an industrial gas turbineengine of a power plant of claim 1, and further comprising the steps of:removing the old electric generator from the power turbine; adding a lowpressure compressor to be driven by the power turbine; adding a variableinlet guide vane assembly to an inlet side of the power turbine; addinga compressed air line connecting the low pressure compressor to the newinlet of the main compressor such that compressed air from the lowpressure compressor flows into the main compressor; and, adding a newelectric generator having around twice the electrical power productionof the old generator to be driven by the high pressure compressor shaft.4. The process for retrofitting an industrial gas turbine engine of apower plant of claim 3, and further comprising the steps of: removing atleast one stage of rotor blades and stator vanes from the maincompressor to optimally match a pressure ratio split between the lowpressure compressor and the main compressor.
 5. The process forretrofitting an industrial gas turbine engine of a power plant of claim3, and further comprising the steps of: adding a gear box between thenew electric generator and the high pressure compressor shaft.
 6. Theprocess for retrofitting an industrial gas turbine engine of a powerplant of claim 1, and further comprising the steps of: removing at leastone stage of the stator vanes form the high pressure turbine; installingnew at least one stage of stator vanes in the high pressure turbine inwhich the new stator vanes have a closed loop cooling circuit; providinga source of compressed air for cooling of the new stage of turbinestator vanes; and, discharging spent cooling air from the new stage ofturbine stator vanes into the combustor that produces the hot gas streamfor the high pressure turbine.
 7. The process for retrofitting anindustrial gas turbine engine of a power plant of claim 6, and furthercomprising the steps of: bleeding off cooling air from the high pressurecompressor; intercooling the cooling air; increasing the pressure of thecooling air to a pressure slightly higher than an outlet pressure of thehigh pressure compressor; and, passing the higher pressure cooling airthrough the closed loop cooling circuit in the new stage of turbinestator vanes.
 8. The process for retrofitting an industrial gas turbineengine of a power plant of claim 6, and further comprising the steps of:compressing ambient air with an external compressor to a pressureslightly higher than an outlet pressure of the high pressure compressor;intercooling the cooling air; and, passing the higher pressure coolingair through the closed loop cooling circuit in the new stage or stagesof turbine stator vanes.
 9. The process for retrofitting an industrialgas turbine engine of a power plant of claim 6, and further comprisingthe steps of: bleeding off compressed cooling air from an outlet of thehigh pressure compressor; intercooling the compressed cooling air;increasing the pressure of the compressed cooling air to a pressureslightly higher than an outlet pressure of the high pressure compressor;and, passing the higher pressure cooling air through the closed loopcooling circuit in the new stage of turbine stator vanes.
 10. Theprocess for retrofitting an industrial gas turbine engine of a powerplant of claim 6, and further comprising the steps of: bleeding offcompressed cooling air from an outlet of the high pressure compressor;increasing the pressure of the compressed cooling air to a pressureslightly higher than an outlet pressure of the high pressure compressor;intercooling the compressed cooling air; and, passing the higherpressure cooling air through the closed loop cooling circuit in the newstage or stages of turbine stator vanes.
 11. The process forretrofitting an industrial gas turbine engine of a power plant of claim6, and further comprising the steps of: bleeding off some of thecompressed air from the compressed air line between the low pressurecompressor and the high pressure compressor for use as the cooling airfor the new stage of turbine stator vanes; and, cooling and compressingthe cooling air to a pressure slightly higher than an outlet pressure ofthe high pressure compressor.
 12. The process for retrofitting anindustrial gas turbine engine of a power plant of claim 1, and furthercomprising the steps of: adding a variable inlet guide vane assembly toboth the main compressor and the low pressure compressor.
 13. A powerplant with a retrofitted industrial gas turbine engine capable ofproducing greater power and at high efficiency, the power plantcomprising: an old main compressor driven by a high pressure turbinewith a combustor; a new inlet for the old main compressor capable ofgreater compressed air flow; re-using the old electric generator; a lowspool with a new low pressure turbine or an old power turbine driven byexhaust gas from the high pressure turbine; a new low pressurecompressor driven by the low pressure turbine; a new compressed air lineconnecting the new low pressure compressor to the new inlet of the highpressure compressor; and, a new variable inlet guide vane assembly forthe new low pressure turbine or the old power turbine.
 14. The powerplant of claim 13, and further comprising: the old main compressor iswithout at least one stage of stator vanes and rotor blades such that apressure ratio is optimally matched between the main compressor and thenew low pressure compressor.
 15. The power plant of claim 13, andfurther comprising: the high pressure turbine has at least one stage ofnew stator vanes with a closed loop cooling circuit; a source ofcompressed cooling air; a compressed air cooling circuit to delivercompressed cooling air to the closed loop cooling circuit of the statorvanes and discharge spent cooling air into the combustor.
 16. The powerplant of claim 15, and further comprising: a new boost compressorbetween the source of compressed cooling air and the stage of statorvanes to increase the pressure of the cooling air; and, a newintercooler between the source of compressed cooling air and the stageof stator vanes to cool the compressed cooling air.
 17. The power plantof claim 13, and further comprising: Replacing the old electricgenerator with a new electric generator driven by the old maincompressor with the new electric generator having a greater electricalpower production than the old electric generator.